6.5 Creedmoor, semi auto, accurate. Pick any 2?

[bert2368]

Originally Posted by Oso Polaris

Bert,

Do you have an adjustable gas block in the new toy?

Not yet! I would certainly consider that, especially if it allowed custom reloading for a bit more snort without beating the $#!? out of the action.

I also am thinking a better trigger is called for, the factory trigger doesn't actually SUCK, it just could be BETTER.

[Oso Polaris]

Originally Posted by bert2368

Not yet! I would certainly consider that, especially if it allowed custom reloading for a bit more snort without beating the $#!? out of the action.

I also am thinking a better trigger is called for, the factory trigger doesn't actually SUCK, it just could be BETTER.

The adjustable gas block will significantly improve the amount of recoil and recoil impulse as well as reduce unnecessary wear on the equipment. Buy an SLR Rifleworks Adjustable Gas Block ($100 on sale). The clamp style if more than adequate (Sentry 7 or 8 depending on barrel thickness at gas port).
https://slrrifleworks.com/sentry-7-c...ble-gas-block/

There is also a gas block alignment tool that makes it idiot proof to ensure proper alignment without the need for calipers or other measurements. It will save you 30min - 1 hour of putzing frustration.
https://www.primaryarms.com/uniquete...igner-ct151130

As far as triggers go there are any number of quality triggers. I use Geiselle in all my guns. Usually the SSAE trigger. However. I bought their new National Match Trigger for my AR10 and its getting pretty close to a Jewel!!! No regrets

[bert2368]

I had found some good reviews of S&B 6.5 CM 140 grain FMJ ammunition.

I have had very good luck accuracy wise with a couple of other S&B products, so I bought some of the S&B 6.5 Creedmoor 140 FMJ.



It is not uniform enough for my use as it came. The first 10 rounds made two fairly tight clusters about 1.5" spread vertically at 100 yards, plus a couple of fliers in random directions at least 2 and 3 inches from any other round!

That caused me to check for loose scope mounts, clean the rifle thoroughly and then go back and try some of the other ammo previously shown to be accurate and generally work to isolate what had happened to blow the accuracy.

Rifle, scope and mounts were fine. Hornady ammo was still as accurate as previously seen.

Time to dissect and measure some of the S&B? Heck yes. See the pic for results- I started with 5 samples randomly pulled from a box chosen at random from a case of 500. I don't need to go any further to know why the accuracy is disappointingly poor.

I used a good quality Mitutoyo dial caliper, Starrett 1" micrometer and an Ohaus Dial-O-Gram scale accurate to 10 milligrams to make the measurements below. All length measurements were re taken several times, bullet/case Dia. measurements repeated at least 3 times at different orientations. Scale was zeroed and zero re-checked against an RCBS weight set at center of each range where measurements were taken (around 2-3 grams for propellant, around 9-10 grams for projectiles & primed cases).

Results and my assessment of what they might mean...



Cartridge OAL varied .002". Base to ogive measurement varied .003". Respectable quality control for commercial ammo, if not competition grade (or as tight as my .221 varmint loads).

Ammo is loaded with a fairly fine grained flattened ball powder, about 80% full by volume. The charge weights were all within 20 milligrams (less than 1/3 grains variation). Not bad QC for cheap commercial ammunition. Considering what mistake would most likely get an ammo manufacturer sued for dammage/injuries, understandable that they were pretty careful here.

Case length was held to a .003" variation. Case weights varied by 360 mg (about 5.5 grains) from highest to lowest, with largest case weight differences proportional to difference in case trim length. No surprises here, ammo has got to fit in the chamber or it will cause complaints. Weights ran up to about 1.5% higher or lower than the median (3% total variation).

But the BULLETS. Not such good QC HERE.

Weights varied by 180 mg from highest to lowest (almost 3 grains). One projectile was out of round by .002". And for a real surprise, one projectile (the heaviest one) was .029" longer than the shortest of the others.

Time to neck size the brass and (carefully) reload with original powder and some good quality USA made projectiles. I would wager that I'll get some better results with that technique.

Major PITA to do that to 22 boxes of ammo...

(Edit)

Pulled down the rest of that box. One of the 15 projectiles was similar to the overweight /over length bullet I found in the first 5.

To make matters worse, the over length projectiles have irregular bases and slightly asymmetrical parting lines between body and boat tail. No way THOSE are going to be accurate.

Got out a couple of boxes of Hornady, Sierra and Barnes bullets, checking for functional OAL in magazine and a similar base to ogive distsnce when loaded.

[Oso Polaris]

Bert,

S&B ammo - Was the bullet or primer sealed in the case?

[bert2368]

Originally Posted by Oso Polaris

Bert,

S&B ammo - Was the bullet or primer sealed in the case?

Neither. This ammunition is NOT assembled the way military ammo is. No crimped primers, no sealants.

I did read your advice on testing to ensure bullets don't get repositioned under recoil or the forces exerted during cycling the bolt, thanks for the suggestions. Will proced with all due caution, have 15 rounds loaded for the next trip to the range.

[Oso Polaris]

Originally Posted by bert2368

Neither. This ammunition is NOT assembled the way military ammo is. No crimped primers, no sealants.

I did read your advice on testing to ensure bullets don't get repositioned under recoil or the forces exerted during cycling the bolt, thanks for the suggestions. Will proced with all due caution, have 15 rounds loaded for the next trip to the range.

Cool - glad that this one step wasn't a PITA!!!! Nothing more fun than using a Q-tip dipped in Acetone to remove tar sealant from inside neck of case.

[bert2368]

Replacing the irregular weight/non symetrical Czech bullets with decent quality bullets works a treat.



The below groups were shot with ammo assembled with brass, primers and powder from the cheap S&B 140grain FMJ ammo

These loads had NOTHING done except pull and replace the projectiles. I did NOT even out the powder loads, they are as sent out from factory. I did NOT do any sizing of the case necks. I set the new bullets at same base to ogive length as the original bullets (2.155"), OAL was fine to feed in a Magpul .308/7.62 NATO magazine.

I marked the second round in each magazine (first round to be loaded automatically) and ejected & measured length after firing first round. The self loading process did NOT move the bullets measurably, no telescoping. Neck tension was "sufficient", even without resize after pulling original bullets.

Below are a couple of 5 round groups at 100 yards.

With Hornady 140 gr. spire point #2630:



With Sierra Game King Spitzer #1730:



Checking the inaccurate 130 grain OTM Federal Gold Medal Match ammo, the base to ogive length is only 2.075". Federal GMM ammo OAL is only .005 shorter than max OAL to feed through my AR10 magazines- The Barnes 120 TTSX I tried were loaded just a bit longer to ogive at 2.100", they shot a LITTLE tighter than the Federal GMM 130, but not as well as the two 140 grain bullets shown above.

I am thinking that this rifle/magazine combination isn't going to get along with the typical nose profiles of modern long range 6.5 bullets.

[Oso Polaris]

The Barnes TTSX bullets are devastating hunting round!!! if it groups for you then look no further for your hunting round

[bert2368]

Oh yes, I have killed 4 white tail deer with the 6.5mm 120 TTSX out of the 6.5-284 NORMA so far. Preaching to the choir here...

Need to play with different seating depths, I would love to have the 120 TTSX work better in the 6.5 CM.

[Oso Polaris]

Originally Posted by bert2368

Oh yes, I have killed 4 white tail deer with the 6.5mm 120 TTSX out of the 6.5-284 NORMA so far. Preaching to the choir here...

Need to play with different seating depths, I would love to have the 120 TTSX work better in the 6.5 CM.

I load the Barnes TAC TSX bullet (110gr) in my 300BO for hogs. I have learned to only take head shots so that I don't destroy good meat. for people that haven't used it I usually explain that there is 4"-6" diameter circle around entry wound that looks like someone poured a jar of grape jelly into it...Hydrostatic shock!!!

I'm glad your AR10 is working well!